The present invention relates to quick-setting, hot-melt adhesive compositions which are solvent-free, reactive compositions which can be applied at relatively low temperatures. Hitherto hot-melt materials including EVA, polyester or polyamide have been used for fast bonding processes and automatic adhesive application requiring quick setting bonds but these have necessitated high application temperatures.
For example, solvent-free reactive polyurethane hot-melt materials, such as are disclosed in DOS 2 609 266, solve the problem of high application temperatures by application of a low-viscosity hot melt at 100.degree. C. which sets by crystallisation. Such adhesive systems exhibit good thermolytic and hydrolytic stability when chain-extended and cross-linked by atmospheric moisture. However, bonds provided by these crystallising polyurethane prepolymers have low elasticity before curing resulting in low initial peel strength immediately after bonding and have a lower setting rate which depends on the crystallisation rate of the polyester used. Other reactive crystalline polyurethane hot melts, such as the adhesive compositions disclosed in DOS 3 236 313, do show a better elasticity in the uncured state but have an undesirably high application temperature (approaching those of conventional hot-melt materials) and exhibit pot life problems at application. It is accordingly an object of the present invention to provide quick-setting, hot-melt adhesive compositions comprising polyurethane pre-polymers which have improved flexibility immediately after bonding whilst being heat stable and resistant to hydrolytic and chemical attack after curing.